This invention relates to the field of fluid pumps. More particularly, it pertains to a Gerotor fluid pump specially suited for pumping hydraulic fluid such as lubricant.
Under normal operating conditions in most machines and dynamic mechanical assemblies, components that translate or rotate at high speed or under load are continuously supplied with lubricant. The surfaces and devices that support these moving components, such as bearings, journals and bushings, require a reliable, continuous supply of lubricating fluid to avoid frictional wear and excessive temperature. Lubricant generally flows to the support surfaces under positive pressure produced by a lubricant pump and returns due to gravity to a sump connected to the pump inlet. Although heat transferred to the lubricant from the support surfaces is at least partially dissipated by convention and conduction, the lubricant's temperature is nonetheless elevated during the lubrication process.
A Gerotor pump, driven by a shaft of the machine or assembly, is frequently used to supply lubricant though a hydraulic circuit to the friction surfaces of the assembly. Lubricant is generally carried from the pump to the friction surfaces through a passage, which may be an axial bore formed in a shaft of the machine, such as the shaft that drives the pump. Typically, Gerotor pumps have been constructed of precision machined aluminum or other metals. Minimizing the weight of the pump, increasing its durability, and providing elevated temperature performance are important considerations in the design of the pump.
A lubrication pump is usually located in a machine or assembly at a position that is hidden from external view and not easily inspected. It is important, therefore, that it operates reliably and has a long service life. The pump should be self-priming, i.e. the pump inlet should be supplied continuously with a source of fluid in order to avoid cavitation at the inlet, which can damage metal surfaces near the low pressure inlet. It is preferred that metal components in this area be avoided and that synthetic materials be used instead to avoid the susceptibility of metals to cavitation damage.
Since the operating temperature of the lubrication pump is approximately 250° F., thermal expansion of the pump components is an important factor that affects operating efficiency of the pump. It has been discovered that the thermal expansion coefficient of nylon when filled with Kevlar or Teflon can be used to increase efficiency of the pump as its operating temperature increases above ambient temperature.
Gerotor pumps having inner and outer gears produced from powdered metal typically require precision machining, thereby adding to their cost and the complexity of production. By using molded gears produced from nylon, Teflon, and Kevlar, machining costs are minimized, and no precision machining is required.